ninth edition TORTORA FUNKE CASE M I C R O B I O L O G Y

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings

PowerPoint® Lecture Slide Presentation prepared by Christine L. Case

M I C R O B I O L O G Y a n i n t r o d u c t i o n

ninth edition TORTORA FUNKE CASE

6 Microbial

Growth


Microbial growth is the increase in number of cells,

not cell size

Microbial Growth


Reproduction in Prokaryotes

Binary fission

Budding

Conidiospores (actinomycetes)

Fragmentation of filaments


Binary Fission

Figure 6.11


Generation Time

Time required for a cell to divide (and its population

to double)

E. coli: 20 minutes (under ideal conditions)

Microbial Growth

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 6.14


The Requirements for Growth: Physical Requirements

Temperature

Minimum growth temperature

Optimum growth temperature

Maximum growth temperature



Temperature

Psychrophiles: cold-loving microbes

Mesophiles: moderate temperature-loving microbes

Thermophiles: heat-loving microbes

Psychrotrophs: capable of growth between about 0O

and 30OC

Cause food spoilage

Hyperthermophiles (extreme thermophiles): optimum

growth temperature of 80OC or higher


Temperature

Figure 6.1


Psychrotrophs

Figure 6.2



pH

Most bacteria grow between pH 6.5 and 7.5

Molds and yeasts grow between pH 5 and 6

Acidophiles grow in acidic environments

Chemical buffers are included in growth media to

neutralize acids and maintain proper pH



Osmotic pressure

Microorganisms obtain almost all their nutrients in

solution from the surrounding water

Hypertonic environments, increase salt or sugar,

cause plasmolysis (shrinkage of the cell’s cytoplasm)

Extreme or obligate halophiles require high osmotic

pressure

Facultative halophiles tolerate high osmotic pressure



Figure 6.4


The Requirements for Growth: Chemical Requirements

Carbon

Structural organic molecules, energy source

Chemoheterotrophs use organic carbon sources

Autotrophs use CO2


The Requirements for Growth: Chemical Requirements Nitrogen

In amino acids and proteins

Most bacteria decompose proteins

Some bacteria use NH4+ or NO3

–

A few bacteria use N2 in nitrogen fixation

Sulfur

In amino acids, thiamine and biotin

Most bacteria decompose proteins

Some bacteria use SO42– or H2S

Phosphorus

In DNA, RNA, ATP, and membranes

PO43– is a source of phosphorus



Trace elements

Inorganic elements required in small amounts

Usually as enzyme cofactors



Oxygen (O2)

Table 6.1




Organic growth factors

Organic compounds obtained from the environment

Vitamins, amino acids, purines, and pyrimidines


Culture Media and Obtaining Pure Cultures


Culture Media

Culture medium: Nutrient material prepared for the

growth of microorganisms in a laboratory

Sterile: contains no living microorganism

Inoculum: microbes introduced into a culture medium to

initiate growth

Culture: microbes that grow and multiply in or on a

culture medium


Agar

Complex polysaccharide

Derived from algae

Used as solidifying agent for culture media in Petri

plates, slants, and deeps

Generally not metabolized by microbes

Liquefies at 100°C

Solidifies ~40°C


Petri dish

Shallow dishes with a lid that nests over the bottom to

prevent contamination


Culture Media

Chemically defined media: Exact chemical composition

is known

Complex media: Extracts and digests of yeasts, meat,

or plants

Nutrient broth (liquid form)

Nutrient agar (when agar is added)


A pure culture contains only one species or strain.

A colony is a population of cells arising from a single

cell or spore or from a group of attached cells.

A colony is often called a colony-forming unit (CFU).


Streak Plate

Figure 6.10a–b

The isolation method most commonly used to get pure

cultures.

• Sterile inoculating loop is dipped into a mixed culture

• Streaked in a pattern over the nutrient medium

• Last cells to be rubbed off the loop are far enough

apart to grow into isolated colonies

• Colonies can be picked up with an inoculating loop and

transferred to a test tube of nutrient medium to form a

pure culture



Streak Plate

Figure 6.10a–b


Measuring Microbial Growth

Direct methods

Plate counts

Filtration

MPN

Direct microscopic count

Dry weight

Indirect methods

Turbidity

Metabolic activity

Dry weight


Direct Measurements of Microbial Growth

Figure 6.19, steps 1, 3


Estimating Bacterial Numbers by Indirect Methods

Turbidity

Figure 6.20

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ninth edition TORTORA FUNKE CASE M I C R O B I O L O G Y